A Prospective, Multicenter, Observational Cohort Study to Evaluate the Efficacy and Safety of a Novel Anti-tumor Drug as a Radiosensitizer in Patients With Advanced Breast Cancer Brain Metastasis.

Inclusion Criteria:

1. Males or females who are at least 18 years of age on the day of signing the informed consent form.
2. Patients with advanced breast cancer that is inoperable and has metastasized to the brain, confirmed by histology or cytology.
3. Patients who are planned to receive, currently receiving, or have completed intracranial radiotherapy after discussion by a multidisciplinary team (MDT) at the stage of brain metastasis.
4. Patients who are planned or currently receiving a systemic treatment regimen with a novel anti-tumor drug selected by the physician, within 3 weeks before radiotherapy, during radiotherapy, or within 3 weeks after completion of radiotherapy. These drugs include:

   ADC drugs (such as T-DXd, T-DM1, etc.), CDK4/6 inhibitors, TKI drugs (such as Pyrotinib, Tucatinib, etc.), Novel chemotherapy drugs (such as Utidelone, Irinotecan liposomes, etc.), Bevacizumab, PD-1/PD-L1 inhibitors, etc.
5. Patients with a traceable medical history during the treatment period.
6. Patients who are able to sign the informed consent form to participate in the study.

Exclusion Criteria:

1. The subject has leptomeningeal metastasis.
2. If the patient has concurrent brain metastasis, the neurological symptoms are too severe to cooperate with radiotherapy.
3. The subject has not signed the informed consent form.
4. Pregnant or breastfeeding women.
5. Other situations deemed by the investigator as unsuitable for inclusion in the study.